Multiplex transmission apparatuses, multiplex transmission networks, and operation method therefor

ABSTRACT

In a synchronous multiplex network including a plurality of multiplex transmission apparatuses, an overhead is passed through intervening multiplex transmission apparatuses such that administration and maintenance operation information is transmitted and received through the overhead between arbitrary multiplex transmission apparatuses. The multiplex transmission apparatus receives a multiplexed signal comprising a payload having a plurality of main signals multiplexed therein and overhead bytes including a plurality of administration and maintenance operation information, performs termination processing for the administration and maintenance operation information and transmission processing for the payload, thereafter converts the multiplexed signal into a different multiplexed signal comprising a payload which has been processed for transmission and a plurality of administration and maintenance operation information, and transmits the different multiplexed signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a con of U.S. patent application Ser. No.08/863,675 filed May 27, 1997 now U.S. Pat. No. 6,169,754, which isincorporated by reference herein as fully as if set forth in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to configurations of digital transmissionapparatuses and configurations of communication networks using thedigital transmission apparatuses, and more particularly toconfigurations of transmission apparatuses for use in a synchronousdigital hierarchy and configurations of communication networks using themultiplex transmission apparatuses.

2. Description of the Related Art

In today's digital transmission networks, the technology ofsynchronization has been advanced to such a degree that a communicationnetwork is synchronized with faster transmission apparatuses employingoptical transmission. For functions and configurations of the digitaltransmission networks and transmission apparatuses, worldwide standardshave been established such that a transmission apparatus and/or acommunication network may be introduced in conformity to the standardsto provide high quality transmission anywhere in the world. Examples ofspecific standards may include the standard (established in 1988) on atransmission system referred to as “SDH” (Synchronous Digital Hierarchy)defined in Recommendation G. 707 and so on by InternationalTelecommunication Union (hereinafter abbreviated as “ITU-T), and thestandard (established in 1991) on a transmission system referred to as“SONET” (Synchronous Optical Network) defined in Standard T1.105 byAmerican National Standard Institute (hereinafter abbreviated as“ANSI”), both of which define the configuration of optical synchronouscommunication systems and functions of transmission apparatuses.

Both SDH and SONET define the processing (transmission,multiplexing/demultiplexing, and so on) of a synchronous multiplexedsignal (frame) which comprises a main signal portion referred to as a“payload” in which digitized main signals are multiplexed, and signalsreferred to as “overheads”, added to the payload, for administration andmaintenance operations for a transmission apparatus and communicationnetwork. The overheads include pointers which are used to perform stuffcontrols such as frame phase synchronization and frequency adjustment toprovide a transmission system which has a less transmission delay and ahigher administration and maintenance operation performance thanconventional digital synchronous transmission apparatuses. The overheadsadded to the frame are classified into a section overhead (SOH) and aline overhead (LOH). The section overhead is used for administration andmaintenance operations for each transmission span between transmissionapparatuses and regenerators (defined as a section), and generated in anapparatus (including a regenerator), transmitted through a transmissionspan, and terminated at a next apparatus. The line overhead is used foradministration and maintenance operations for each transmission intervalbetween transmission apparatuses which process multiplexed main signals(defined as a line). The line overhead is generated in a transmissionapparatus, transmitted through transmission spans and regenerators, andterminated at a next multiplexing apparatus. Examples of transmissionapparatuses and networks adopting the above-mentioned SDH or SONET aredescribed in JP-A-4-79628 and JP-A-5-114892.

In a transmission network in conformity to SDH or SONET, multiplexersmay be occasionally connected to each other on a transmission linethrough regenerators. For carrying out the administration andmaintenance operations between the multiplexers in such a transmissionnetwork, the line overhead is used to transmit and receive data andspeech signals necessary to the administration and maintenanceoperations between the multiplexers. For example, D-bytes referred to as“data communication channels” and E-bytes referred to as “orderwires” ofthe line overhead are used to transmit and receive such data and speechsignals between the multiplexers. Specifically, when a multiplexer onthe transmission side inserts data and speech information into D4-D12bytes and E2 byte of a line overhead and transmits the line overheadonto a transmission line, the line overhead is terminated at adestination multiplexer through the transmission line and regenerators,thereby carrying out the administration and maintenance operationsbetween the multiplexers.

As the number of subscribers increases in the transmission network or asan increased amount of signals is communicated through the transmissionnetwork, extension and/or modifications in the transmission network,such as installation of additional multiplexers and replacement to thetransmission network to a faster transmission line, may be required forsupporting the increase in subscribers and the amount of communicatedsignals. For example, if the amount of communications increases, theexisting transmission network is reconfigured, wherein similarmultiplexers to those so far used are additionally installed in thetransmission network, and a plurality of faster and larger-scaledmultiplexers are introduced for processing signals in place ofregenerators to modify the transmission network so that the multiplexersare connected through faster transmission line in the transmissionnetwork.

However, the reconfiguration of the transmission networks as mentionedabove results in a problem involved in SDH and SONET standards.Specifically, since the line overhead is terminated at each transmitteraccording to SDH and SONET standards, an overhead outputted from anexisting multiplexer may be terminated at an additionally installedfaster multiplexer, so that the overhead is not transmitted to a far-endmultiplexer which has so far received this overhead. In other words, thereconfiguration results in a lack of the administration and maintenanceoperations previously performed between the multiplexers before thereconfiguration. Thus, while the transmission capability of thetransmission network for transmitting main signals is improved by thereconfiguration of the transmission network, the reconfiguration causeschanges in the administration and maintenance operation capability ofthe transmission network, such as lack of the administration andmaintenance operations so far performed between transmissionapparatuses. Since administration and maintenance operation informationpreviously provided is no longer available to a craft person dedicatedto the maintenance of the transmission network, the craft person maysuffer from quite inconvenient situations.

SUMMARY OF THE INVENTION

It is an object of the present invention to prevent changes inadministration and maintenance operation capability due to areconfiguration of a transmission network as mentioned above, andspecifically to provide a transmission apparatus and a transmissionnetwork having an administration and maintenance operation capabilitywhich is not affected by any modification to the transmission network orwhich enable more flexible and high performance administration andmaintenance operations in a simple configuration.

More specifically, the present invention provides a transmissionapparatus which additionally has a function of passing through anoverhead instead of processing the overhead standardized by SDH andSONET. The present invention also provides a transmission network, whichis flexible and superior in administration and maintenance operationperformance, wherein the transmission network uses transmissionapparatuses as mentioned above, such that arbitrary transmissionapparatuses in the transmission network are permitted to transmit andreceive an arbitrary overhead therebetween. The present invention alsoprovides a method of operating the configuration for the transmissionnetwork.

In a more detailed aspect, the present invention provides circuits andapparatus for use in a digital transmission apparatus, in a simplestructure, for selectively cross-connecting a received tributaryoverhead and transmitting the cross-connected overhead to a far-endtransmission apparatus. The present invention also allows for atributary overhead containing information which cannot be interpreted ata far-end destination apparatus simply by passing the overhead throughintervening apparatuses, and provides circuits and apparatus, in asimple structure, for converting a tributary overhead into informationusable by a far-end destination apparatus and for transmitting theconverted information to the far-end destination apparatus. Inparticular, the present invention provides simple circuits and apparatusfor accurately notifying the number of transmission errors, if any, in atributary through which an overhead is transmitted and received, toenable the management of transmission quality.

Moreover, the present invention provides a method of selectivelycross-connecting an overhead and transmitting and receiving thecross-connected overhead between selected multiplexers, and a method ofdetecting and notifying transmission errors which have occurred in atributary.

To solve the problems mentioned above, a multiplex transmissionapparatus according to the present invention receives a multiplexedtributary signal comprising a payload having a plurality of main signalsmultiplexed therein and overhead bytes including a plurality ofmaintenance information associated with administration and maintenanceoperations, performs termination processing for the administration andmaintenance operation information and transmission processing for thepayload, thereafter converts the multiplexed tributary signal into amultiplexed high-speed signal comprising a payload including mainsignals which have been processed for transmission and a plurality ofadministration and maintenance operation information, and transmits themultiplexed high-speed signal. The multiplex transmission apparatuscomprises a circuit or a apparatus for selecting predeterminedmaintenance information from the plurality of maintenance informationincluded in the received multiplexed tributary signal, and inserting thepredetermined maintenance information into an overhead byte in themultiplexed high-speed signal on the high-speed transmission side tothereby pass the predetermined maintenance information through themultiplex transmission apparatus.

Specifically, the multiplex transmission apparatus comprises an overheadpassing circuit or a passing apparatus for passing maintenanceinformation which is composed of an extraction circuit or an extractionapparatus for extracting predetermined maintenance information from theplurality of maintenance information included in the receivedmultiplexed tributary signal, and an insertion circuit or an insertionapparatus for inserting extracted maintenance information into apredetermined location in the overhead bytes of the multiplexedhigh-speed signal to be transmitted. The overhead passing circuit orapparatus may be additionally provided with an cross-connecting circuitor cross-connecting apparatus for cross-connecting extracted maintenanceinformation.

Also, the multiplex transmission apparatus receives a plurality ofmultiplexed tributary signals each comprising a payload and overheadbytes including a plurality of maintenance information associated withadministration and maintenance operations, performs terminationprocessing for the plurality of maintenance information and multiplexingof the plurality of payloads in a payload having a larger multiplexingdegree, converts the plurality of multiplexed tributary signals into amultiplexed high-speed signal comprising the larger payload and overheadbytes, added to the large payload, having a size larger than theoverhead bytes on the tributary side including a plurality ofmaintenance information associated with administration and maintenanceoperations, and transmits the multiplexed high-speed signal. Themultiplex transmission apparatus comprises an overhead passing circuitor a passing apparatus for passing maintenance information which iscomposed of an extraction circuit or an extraction apparatus forextracting predetermined maintenance information from the plurality oftributary maintenance information, an cross-connecting circuit or across-connecting apparatus for cross-connecting information extracted bythe extraction circuit or apparatus, and an insertion circuit or aninsertion apparatus for inserting an output of the cross-connectingcircuit or apparatus into a predetermined location of the high-speedoverhead bytes, wherein the maintenance information received from theplurality of transmission paths is collectively transferred or passed.

A far-end transmission apparatus connecting this multiplex transmissionapparatus through high-speed transmission line comprises an overheadpassing circuit or passing apparatus which is composed of an extractioncircuit or an extraction apparatus for extracting predeterminedmaintenance information from a plurality of high-speed maintenanceinformation, a cross-connecting circuit or a cross-connecting apparatusfor cross-connecting information extracted by the extraction circuit orapparatus, and an insertion circuit or an insertion apparatus forinserting an output of the cross-connecting circuit or apparatus into apredetermined location of the tributary overhead bytes, wherein uponreceiving high-speed overhead bytes including maintenance informationcollectively transferred thereto, these signals are extracted,cross-connected, and inserted into predetermined locations of aplurality of tributary overhead bytes to be transmitted onto a pluralityof tributary transmission lines.

Here, each of the foregoing multiplex transmission apparatuses processesthe multiplexed signals defined in Recommendation G. 707 ofInternational Telecommunication Union or in Standard T1. 105 of AmericanNational Standard Institute. Maintenance information to be passed isthat included in a section overhead and a line overhead of tributaries.The maintenance information to be passed is transferred in a lineoverhead of a multiplexed high-speed signal. In addition, when thesemultiplexers are directly connected without regenerators, a sectionoverhead is also used to pass or transfer an increased amount ofmaintenance information. When E byte, F byte, D byte, K byte, and Zbyte, defined by the standard, are to be passed as maintenanceinformation, these bytes are selected and passed as they are.

On the other hand, as a configuration for passing information on numberof errors on a transmission path such as B bytes defined by thestandard, a transfer circuit or a transfer apparatus is provided asfollows. The transfer circuit or apparatus, upon detecting the number oferrors which have occurred on a receiving tributary transmission line,inserts this number of occurring errors into an overhead byte of amultiplexed high-speed signal such that the number of errors istransferred in the multiplexed high-speed signal. Then, a far-endmultiplex transmission apparatus which receives transferred maintenanceinformation comprises an extraction circuit or an extraction apparatusfor extracting the number of transmission errors of near-end tributary,an adder circuit or an adding apparatus for adding the extracted numberof transmission errors of the near-end tributary and the number ofhigh-speed transmission errors detected by this multiplex transmissionapparatus, and a circuit or an apparatus for inserting the additionresult into a second high-speed signal overhead and transferring theoverhead, or for adding the number of transmission errors correspondingto the addition result to an error detecting signal of tributary. Foranother configuration or method, a multiplex transmission apparatuslocated in the middle of a high-speed transmission line transfer thenumber of transmission errors in tributary, and a multiplex transmissionapparatus comprises detector circuit or a detecting apparatus fordetecting the number of errors which have occurred in a high-speedtransmission lines, an extraction circuit or an extraction apparatus forextracting the number of transmission errors of the near-end tributary,an adder circuit or an adding apparatus for adding the extracted numberof transmission errors and the number of transmission errors detected bythe detector circuit or apparatus, and a circuit or an apparatus foradding the number of transmission errors corresponding to the additionresult to an error detecting signal of tributary.

Furthermore, to solve the problems mentioned above, a multiplextransmission network according to the present invention employs theapparatus as described above for a multiplex transmission apparatus forpassing arbitrary maintenance information of the tributaries throughintermediate multiplexers between arbitrary multiplex transmissionapparatuses, so that the arbitrary multiplex transmission apparatusestransmit and receive arbitrary maintenance information of thetributaries therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a frame structure diagram illustrating the structure of aframe of a tributary multiplexed signal (OC-12);

FIG. 2 is a frame structure diagram illustrating the structure of aframe of a high speed multiplexed signal (OC-192);

FIG. 3 is a function explanation diagram for explaining the functions ofoverheads in a multiplexed signal;

FIGS. 4A, 4B and 4C are network configuration diagrams for explainingthe configuration of transmission networks and overhead processingintervals;

FIG. 5 is a block configuration diagram illustrating the configurationof a transmission apparatus according to the present invention;

FIG. 6 is an overhead structure diagram for explaining how tributaryoverheads are passed through a transmission apparatus (multiplexer)according to the present invention;

FIG. 7 is an overhead structure diagram for explaining how tributaryoverheads are passed through a transmission apparatus according to thepresent invention;

FIG. 8 is an operation explanation diagram for indicating a calculationarea of a tributary overhead (B2 bytes) in the transmission apparatusaccording to the present invention;

FIG. 9 is a network configuration diagram illustrating the configurationof a transmission network employing the transmission apparatusesaccording to the present invention;

FIG. 10 is a block configuration diagram illustrating the configurationof another transmission apparatus (ADM) according to the presentinvention;

FIGS. 11A and 11B are network configuration diagrams illustrating theconfiguration of transmission networks employing other transmissionapparatuses according to the present invention;

FIGS. 12A and 12B are operation explanation diagrams for explaining theconfiguration of transmission error detection using a tandem connectionin a transmission network employing the transmission apparatusesaccording to the present invention; and

FIG. 13 is a network configuration diagram illustrating theconfiguration of a transmission network using a tandem connectionemploying the transmission apparatuses according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of transmission apparatuses as well as embodiments oftransmission systems and networks according to the present inventionwill hereinafter be described in detail with reference to theaccompanying drawings.

It should be first noted that the embodiments of the present inventionare described, as an example, with reference to transmission apparatusesand transmission systems mainly used in conformity to SONET. While aconventional transmission system is such that an overhead of atransmission frame is terminated at each apparatus, a transmissionapparatus of the present invention has a function of passing a tributaryoverhead therethrough to enable desired apparatuses within atransmission network to transmit and receive the overhead, therebymaking it possible to improve the administration and maintenanceoperation performance of the transmission apparatus. Transmissionapparatuses and transmission systems using the SDH will also havesubstantially the same configurations.

For facilitating the understanding of the present invention, theconfigurations and operations defined by SONET and SDH are brieflyexplained prior to descriptions on the configurations and operations oftransmission apparatuses and transmission systems according to thepresent invention.

FIGS. 1 and 2, which are frame structure diagrams illustrating thestructures of frames in multiplexed signals defined by SONET, illustratethe configurations of multiplexed signals of OC-12 (622.08 Mb/s) andOC-192 (9953.28 Mb/s). FIG. 3 is an explanatory diagram showingfunctions of respective overhead bytes included in a multiplexed signal.In FIGS. 1-3, signals in columns 1-36 (OC12) or in columns 1-576(OC-192) constitute an overhead (see FIG. 3 as for functions ofrespective bytes. Undefined bytes are indicated by “x” in FIGS. 1 and2), and the remaining area constitutes a payload portion in which mainsignals are multiplexed.

FIGS. 4A-4C are network configuration diagrams for explaining theconfigurations of transmission networks adopting SDH or SONET andtransmission intervals through which overheads are transmitted. Withineach of the overheads in the multiplexed signals, rows 1-3 constitute aso-called section overhead which is associated with administration andmaintenance operations for each transmission span (defined as a“section”) between transmission apparatuses and/or regenerators. Anoverhead generated in an apparatus (including a regenerator) istransmitted through a transmission span and terminated at a nextapparatus (as indicated by an arrowed thin solid line in FIG. 4A).Within consecutive overhead, rows 5-9 constitute a so-called lineoverhead which is associated with administration and maintenanceoperations for consecutive transmission spans (defined as a “line”)between transmission apparatuses which are to process multiplexed mainsignals. An line overhead generated in a transmission apparatus istransmitted through transmission spans and regenerator(s), andterminated at a next transmission apparatus (as indicated by an arrowedfat solid line in FIG. 4A). Bytes in the fourth row of the overheadserve as pointers.

In the transmission network illustrated in FIG. 4A, a multiplexer B(2001) and a multiplexer C (2004) are connected by an OC-12 transmissionline through regenerators 2002, 2003. For example, when D bytes referredto as data communication channels and E-byes referred to as orderwiresare to be transmitted and received for administration and maintenanceoperations between the multiplexers B (2001) and C (2004), one of themultiplexers (for example, B) inserts data and speech signals requiredto the maintenance operation into D4-D12 bytes and E2 byte in a lineoverhead and transmits the line overhead onto the OC-12 transmissionline. Since the line overhead is transmitted through the OC-12transmission line and regenerators and terminated at the multiplexer (Cin FIG. 4A) on the reception side, the administration and maintenanceoperations are carried out between the multiplexers B (2001) and C(2004).

However, if the number of subscribers increases or if the amount oftransmitted and received signals is increased, installation ofadditional multiplexers and modifications to the transmission networkmay be required corresponding to the increase in subscribers or signals.FIG. 4B illustrates an example of a modified network, where multiplexerscorresponding to the multiplexers B (2001), C (2004) are additionallyinstalled (for simplicity, one each of the multiplexers B (2001), C(2004) only is illustrated in FIG. 4B), while a plurality of high speedand large-scaled multiplexers E (2008), F (2009) are introduced in placeof the regenerators 2002, 2003 and connected by a high speedtransmission path OC-192 for processing a larger amount of signals at ahigher rate, thus modifying the transmission network.

When the transmission network is modified from the configurationillustrated in FIG. 4A to the configuration illustrated in FIG. 4B dueto an increase in the amount of communications, an overhead from themultiplexer B (2001) is terminated at the multiplexer E (2008) becauseSDH or SONET defines that a line overhead is terminated at eachmultiplexer. If no countermeasures were taken, the modification in thetransmission network would result in lack of the administration andmaintenance operations previously performed between the multiplexers B(2001) and C (2004) using the overhead before the installation of theadditional multiplexers (FIG. 4A).

To solve this problem, the present invention provides each multiplexerwith a function of passing a tributary overhead therethrough, asillustrated in FIG. 4(C). Then, by building a communication network withthe multiplexer of the invention, an overhead can be transmitted andreceived between desired apparatuses within a transmission system,thereby making it possible to improve the administration and maintenanceoperations of the transmission system. In the following, thetransmission apparatus and the transmission system as well as anoverhead transmission/reception method according to the presentinvention will be described in detail in terms of their configurationsand operations.

FIG. 5 is a block configuration diagram illustrating an embodiment of amultiplexer according to the present invention. The multiplexer of thepresent invention accommodates a plurality of tributary multiplexedsignals each including overheads and multiplexed main signals and a highspeed multiplexed signal including overheads and multiplexed mainsignals to perform processing such as termination, replacement, and soon of overheads in each multiplexed signal as well as demultiplexes themultiplexed main signals in the plurality of tributary multiplexedsignals and the multiplexed main signal in the one high speedmultiplexed signal. For example, the multiplexer of the presentinvention accommodates 16 OC12s (622.08 Mb/s, see FIG. 1) as tributarymultiplexed signals, and performs multiplexing/demultiplexing of mainsignals between the tributary multiplexed signals and the high speedmultiplexed signal OC-192 (9953.28 Mb/s, see FIG. 2) and overheadprocessing as defined by SONET. In addition, the multiplexer passes atributary overhead in a tributary multiplexed signal inputted thereto.It is of course understood that the foregoing is a mere example, andmultiplexed signals to be accommodated may be transmitted at any otherrate than OC-1˜192 or the rate defined by SDH, and the number ofmultiplexed signals to be accommodated may be varied depending on thetype of multiplexed signals to be accommodated.

In FIG. 5, the multiplexer according to the present invention comprisesM sets of tributary signal transmission/reception units 10-1˜10-M forinputting and outputting tributary multiplexed signals to processoverheads and main signals included therein; a set of high speed signaltransmission/reception unit 11 for inputting and outputting a high speedmultiplexed signal to process overheads and main signals includedtherein; a main signal multiplex/demultiplex convertor unit 100 formultiplexing/demultiplexing and converting the main signals in thetributary multiplexed signals and the main signals in the high speedmultiplexed signal; overhead processing units 300 (300-1, 300-2),constituting a feature of the present invention, each forcross-connecting overheads included in each of the tributary multiplexedsignals and the high speed multiplexed signal and for passing thecrossconnected overheads through the multiplexer itself; and a controlunit 400 for controlling the entire multiplexer. The multiplexer iscomposed of the above components to perform multiplexing/demultiplexingand conversion of the signals and overhead processing.

More specifically, each of the tributary signal transmission/receptionunits 10-1˜10-N comprises a SOH (section overhead) termination unit20-1˜20-N for performing the reception of a tributary signal and theprocessing for a received section overhead and for extracting a portionof section overhead bytes which is passed therethrough and transmittedto far end multiplexer; a LOH (line overhead) termination unit 30-1˜30-Nfor processing a received line overhead and for extracting a portion ofline overhead bytes in a manner similar to the section overhead; a LOHinsertion unit 80-1˜80-N for adding transmitted line overhead bytes andfor inserting line overhead bytes transmitted from far end multiplexer;and a SOH insertion unit 90-1˜90-M for adding transmitted sectionoverhead bytes, for inserting section overhead bytes transmitted fromfar end multiplexer, and for transmitting a tributary signal. The highspeed transmission/reception unit 11 comprises a high speed signal SOHtermination unit 60; a LOH termination unit 70; a LOH insertion unit 40;and a SOH insertion unit 50, all of which are similar to thecorresponding units in the tributary signal transmission/reception unit10. Each of the overhead processing units 300-1, 300-2 comprises anoverhead multiplex unit 110, 130 for collecting overheads extracted fromeach multiplexed signal by the transmission/reception unit (10-1˜10-M,11); a space switch unit 200, 210 for crossconnecting collectedoverheads in accordance with predetermined rules in order to transmitthe overheads to far-end multiplexer; and an overhead demultiplex unit120, 140 for distributing the crossconnected overheads to the LOHinsertion units or to the SOH insertion units of the respectivemultiplexed signal transmission/reception units (10-1˜10-M, 11). Withthe configuration mentioned above, the present invention provides amultiplexer which accommodates tributary multiplexed signals and a highspeed multiplexed signal for multiplexing/demultiplexing main signalsincluded therein, passes therethrough certain tributary overheads, whichhave been previously determined in a transmission system using themultiplexers, and processes (terminates/adds) the overheads, so as toenable desired multiplexers to use the overheads therebetween, thusmaking it possible to provide a multiplexer which is superior inadministration and maintenance operation capability as well as achievesa highly usable and flexible system configuration.

In the following, the configuration and operation of the multiplexer andthe operation of the transmission system according to the presentinvention will be described in connection with an example in whichoverheads in 15 multiplexed signals within tributary signals (orderwiresE1, E2, data channels D1-D12, transmission switching control bytes K1,K2, inter-line (apparatus-to-apparatus) error administration byte B2)are passed through a multiplexer which accommodates a high speedmultiplexed signal through OC-192 and tributary multiplexed signalsthrough 16 OC12s, and used between 15 pairs of transmission apparatuseswhich use the tributary multiplexed signals (between the multiplexers Band C illustrated in FIG. 4B).

FIGS. 6 and 7 are overhead structure diagrams illustrating overheads ina high speed signal used in the multiplexer of this embodiment, intowhich certain overheads in tributary signals are inserted so that theoverheads are passed to far end multiplexer. Specifically, FIG. 6illustrates a general configuration of the overheads and a detailedconfiguration of a portion of the overheads, and FIG. 7 illustrates adetailed configuration of the remaining overheads.

First explained is a multiplexing operation for receiving tributarymultiplexed signals, converting them into a high speed multiplexedsignal, and transmitting the high speed multiplexed signal.

The SOH termination units 20-1˜20-M and the LOH termination units30-1˜30-M of the respective tributary signal transmission/receptionunits 10-1˜10-M perform normal termination processing for overheads ofreceived multiplexed signals in a manner similar to that performed by anormal multiplexer, and send main signals to the main signalmultiplex/demultiplex convertor unit 100. Here, the normal terminationprocessing refers to a check for the normality of a section and a linebetween the multiplexer itself and a far end tributary transmissionapparatus on the tributary multiplexed signal transmission side, whereinthe synchronization of the tributary multiplexed signals is establishedusing A byte, and erroneous signals are checked by B1 byte, by way ofexample. In other words, the processing associated with administrationand maintenance operations of the tributary line or section is performedusing overheads, for example, defined by ANSI T. 105. The main signalsof the tributary multiplexed signals are multiplexed in main signals ofa high speed signal in accordance with multiplexing rules (for example,mapping from FIG. 1 to FIG. 2) previously determined in the main signalmultiplex convertor unit 100. On the other hand, the multiplexer of thepresent invention passes a portion of these tributary overheads for usebetween desired multiplexers, so that the SOH termination units20-1˜20-M and the LOH termination units 30-1˜30-M drop receivedoverheads (except for B2 bytes) as they are so as to transmit theoverheads to the overhead processing unit 300-1. Since B2 bytes cannotbe simply passed for the reason later described, each of the LOHtermination units 30-1˜30-M detects the number of errors in a tributaryline detected as normal B2 bytes termination processing and transmitsthe encoded number of detected errors to the overhead processing unit300-1.

The overhead processing unit 300-1 performs cross-connecting andprocessing for selecting a portion of the tributary overheads andinserting the selected tributary overheads into an undefined area ofoverheads in a high speed multiplexed signal to be transmitted, in orderto pass therethrough the selected portion of the tributary overheadsreceived by the multiplexer to transmit to far end multiplexer. Theoverhead multiplex unit 110 collects overheads transmitted from therespective tributary signal transmission/reception units 10-1˜10-M.Specifically, when tributary multiplexed signals are 16 OC12s, theoverheads formatted as illustrated in FIG. 1 are sent from therespective tributary signal transmission/reception units 10-1˜10-M, sothat the respective units 10-1˜10-M are sequentially accessed using amultiplexer in the multiplex transmission apparatus to select tributaryoverheads from the respective units 10-1˜10-M, which are to be passed,and the selected overheads are grouped in accordance with the type ofoverheads. As an example, D4 bytes (see FIG. 1) located in the sixthrow, the first column of respective tributary multiplexed signals arecollected and mapped in the high speed multiplexed signal from the fifthcolumn to the 61th column of the sixth row (see 1000, 1002 in FIG. 6),such that the D4 bytes are passed by means of the high speed multiplexedsignal. In this way, overheads of the tributary multiplexed signals aregrouped into respective types and inserted into undefined bytes in highspeed multiplexed bytes, so that the respective units are sequentiallyaccessed to collect each type of overheads. More specifically, in theexample given above, multiplexing is performed such that only the D4bytes in the respective tributary multiplexed signals are collected. Inaddition, the multiplexer in the multiplex transmission apparatus may beprovided with a buffer on the input side thereof for enabling themultiplexing even if the respective tributary multiplexed signals aredifferent in the frame phase. Alternatively, the respective units mayalign the phases of signals to be sent to the overhead multiplex unit110. While the B2 bytes have been described to be received after theprocessing in the LOH termination units, the B2 bytes themselves may bereceived from the LOH termination units so that the above-mentionedprocessing is performed in the overhead multiplex unit 110.

The space switch unit 200 crossconnects the tributary overhead bytestransmitted thereto from the overhead multiplex unit 110 so as tofurther rearrange the tributary overhead bytes. While the space switchunit is used in this embodiment, a time switch may of course be usedinstead. Any switch may be used as long as it can crossconnect thetributary overheads for selection, reordering, and so on, such that theoverheads received from respective tributary multiplexed signals can beinserted into predetermined ones of undefined bytes in a high speedmultiplexed signal. Specifically, in this embodiment, out of 16tributary multiplexed signals on OC12s, overheads of 15 multiplexedsignals (1-15) are passed, so that the space switch unit 200 selectsonly overheads to be passed within the multiplexed signals (1-15) fromthe output of the overhead multiplex unit 110. The selected overheadsinclude, for example, orderwires E1, E2, data channels D1-D12, automaticprotection switching control bytes K1, K2, and line(multiplexer-to-multiplexer) error checking byte B2 (see 1000-1004,1100-1107, and 1200-1208 in FIGS. 6 and 7). Also, as previouslyillustrated in FIG. 1, D1 byte located nearer to the head of the framethan D4 byte is inserted into the high speed multiplexed signal afterpassing through the multiplexer later than D4 byte (see 1000, 1001, 1004in FIG. 6). In other words, the space switch unit 200 also rearrange theorder of tributary overheads to be passed such that a specified type oftributary overhead can be inserted into a previously specified one ofundefined bytes in a high speed overhead area.

The overhead demultiplex unit 120 receives tributary overhead bytes sentfrom the space switch unit 200, and demultiplexes the received overheadsinto a section overhead and a line overhead using a demultiplexer aswell as demultiplexes the received overheads such that they are insertedinto previously determined bytes in an overhead area of the high speedmultiplexed signal illustrated in FIGS. 6 and 7, and transfers thedemultiplexed overheads to the high speed signal transmission/receptionunit 11. Taking D4 byte of each tributary multiplexed signal as anexample, the D4 byte of each tributary multiplexed signal is separatedfrom each tributary multiplexed signal such that D4 bytes of therespective tributary multiplexed signals are inserted into every fourcolumns of the overhead area in the high speed multiplexed signal fromthe fifth column to the 61st column of the sixth row, as indicated by1000 and 1002 in FIG. 6.

The high speed signal transmission/reception unit 11 generates overheadbytes for use in a section interval and a line interval of the highspeed transmission side, by means of the SOH insertion unit 50 and theLOH insertion unit 40, in a manner similar to a normal multiplexer. Inaddition, the high speed transmission/reception unit 11 inserts theoverhead extracted by the tributary signal reception unit and receivedfrom the overhead demultiplex unit 120 into previously specifiedundefined bytes in a line overhead of a high speed signal, asillustrated in FIGS. 6 and 7, to create overheads to be transmittedwhich are added to main signals of the high speed signal multiplexed bythe main signal multiplex/demultiplex convertor unit 100 to produce ahigh speed multiplexed signal which is then transmitted from the highspeed signal transmission/reception unit 11. It should be noted that inthis embodiment, if a regenerator is located in the middle of atransmission path, a section overhead is terminated at the regenerator,so that overheads extracted by the tributary signal reception unit areinserted only into a line overhead area of the high speed signal. Ofcourse, if there is no regenerator in the middle of a transmission lineso that a section overhead is not terminated up to a destinationtransmission apparatus, undefined bytes in a high speed section overheadarea may be used for inserting the extracted tributary overheadsthereinto. In this case, a larger number of overheads of tributarymultiplexed signals can be passed.

Next explained is the operation on the demultiplexing side forconverting a received high speed multiplexed signal into tributarymultiplexed signals and transmitting the tributary multiplexed signals.

The SOH termination unit 60 and the LOH termination unit 70 of the highspeed transmission/reception unit 11 terminate overheads in a receivedhigh speed multiplexed signal, similarly to a normal demultiplexer, tosend main signals to the main signal multiplex/demultiplex convertorunit 100, in a manner similar to the tributary signaltransmission/reception unit 10. The main signals are demultiplexed bythe main signal multiplex/demultiplex convertor unit 100 into mainsignals of tributary signals. On the other hand, since the receivedoverheads include those transmitted from a far end multiplexer, whichare to be passed for use as tributary overheads, the SOH terminationunit 60 and the LOH termination unit 70 drop the received overheads asthey are, and transmits them to the overhead processing unit 300-2.

The overhead processing unit 300-2 performs cross-connecting andprocessing for selecting overheads to be inserted into predeterminedlocations in overheads of each tributary multiplexed signals in order topass a portion of the received overheads for transmission to anothertributary transmission apparatus. Thus, the overhead processing unit300-2 performs, on the demultiplexing side, similar processing to thatof the overhead processing unit 300-1 on the multiplexing side in thereverse order. Specifically, the overhead multiplex unit 130 collectsoverheads which have passed through from the far end multiplexer andreceived by the high speed signal transmission/reception unit 11, andthe space switch unit 210 crossconnects the overheads sent thereto fromthe overhead multiplex unit 130 so as to again rearrange them. Also, theoverhead demultiplex unit 140 demultiplexes the overheads sent from thespace switch unit 210 into a section overhead and a line overhead, anddemultiplexes the overheads such that they are inserted into thepreviously specified bytes in the overhead area of each tributarymultiplexed signal illustrated in FIG. 1, and transfers thedemultiplexed overheads to the respective tributary signaltransmission/reception units 10-1˜10-M.

Each of the M sets of tributary signal transmission/reception units10-1˜10-M generates overhead bytes for use in a section interval and aline interval of tributary, in a manner similar to a normal multiplexer,by means of the SOH insertion unit 80-1˜80-M and the LOH insertion unit90-1˜90-M, and inserts overheads extracted by the high speed signalreception unit and received from the overhead demultiplex unit 140 intopreviously specified overhead bytes in the line overhead area of thetributary signal, as illustrated in FIG. 1, to create overheads to betransmitted, which are added to tributary main signals demultiplexed bythe main signal multiplex/demultiplex convertor unit 100 to generate atributary multiplexed signal which is then transmitted to the tributarytransmission line.

Next, the processing of passing the B2 bytes in the transmissionapparatus capable of passing received tributary overheads to far endtransmission apparatus, in accordance with the present invention, willbe explained in connection with the multiplexer used in the foregoingembodiment.

FIG. 8 is an operation explanation diagram for explaining a B2-bytecalculation area for detecting transmission errors in a line interval ina transmission apparatus used in conformity to SONET or SDH. Thetransmission apparatus used in conformity to SONET or SDH uses a pointerlocated in the overhead area as illustrated in FIG. 1 (H-bytes on thefourth row) to identify the phase of a multiplexed signal for signalprocessing such as multiplexing/demultiplexing, in order to reduce adelay of the multiplexed signal. Each transmission apparatus onlyupdates the pointer to a frame forming a multiplexed signal for againidentifying the frame, and does not adjust the phase of the frame on anapparatus-by-apparatus basis as does a conventional transmissionapparatus. For this reason, a pointer update causes a deviation betweenthe B2 calculation area of a received multiplexed signal and the B2calculation area of a multiplexed signal to be transmitted, asillustrated in FIG. 8, whereby even if received B2 bytes are passed in amanner similar to other overhead bytes, a transmission apparatusreceiving overheads cannot correctly detect errors which is notified bythe received B2 bytes.

Stated another way, since the B2 bytes cannot be directly passed asmentioned above, the multiplexing side of the multiplexer is configuredsuch that the respective LOH termination units 30-1˜30-M of thetributary signal transmission/reception units read (terminate) the B2bytes to determine the number of detected errors, and pass a signalencoding the number of detected errors (designated by “j” in thefollowing explanation) to notify a destination transmission apparatus ofthe number of errors. Specifically, the B2 bytes of each tributarymultiplexed signal (first to 12th columns on the fifth row in FIG. 1)are terminated to create a signal (indicative of the number of errors j)which is inserted into undefined bytes in the overhead area of a highspeed multiplexed signal (1103 in FIG. 7), and then transmitted in thehigh speed multiplexed signal.

On the demultiplexing side of the multiplexer, the signal indicative ofthe number of errors j cannot be sent to a tributary as it is, in amanner similar to other overhead bytes, because it is different from B2bytes definition, so that the number of errors cannot be detected in thetributary far end apparatus. In addition, it is the number of errorswhich have occurred between a transmission path between desiredtransmission apparatuses (between the transmission apparatuses B and Cin FIG. 4B) that is desired to be transmitted and received. However,since the value of j does not include the number of errors which haveoccurred on the high speed transmission line between the multiplexers,the high speed line errors are also considered. Thus, the demultiplexingside of the multiplexer of this embodiment is configured to perform thefollowing processing in addition to the processing described above inconnection to the processing performed on the B2 bytes.

First, the LOH termination unit 70 of the high speed signaltransmission/reception unit 11 reads (terminate) the B2 bytes fordetecting transmission errors between the high speed multiplexers (theB2 bytes have been defined in the original high speed multiplexed signaland are shown in the first to 192nd columns of the fifth row in thestructure diagrams of FIGS. 2 and 6) to find the number of errors i. TheLOH termination unit 70 also separates the encoded number of detectederrors j from a line overhead (1103 in FIG. 6) of the high speed signal,and calculates the sum k of i and j.

Next, the overhead multiplex unit 130 of the overhead processing unit300-2 multiplexes this k value with other overhead bytes and transmitsthem to the space switch unit 210. The space switch unit 210 rearrangesthe transferred overhead bytes so as to be directed to the respectivetributary signal transmission/reception units. The overhead demultiplexunit 140 demultiplexes the overhead bytes sent from the space switchunit 210 into section overheads and line overheads which are transferredto the M sets of tributary signal transmission/reception units10-1˜10-M.

Then, the LOH insertion units 80-1˜80-M each generate B2 parities forone frame to be transmitted, invert a number of bits corresponding tothe value of k, insert the B2 bytes as an overhead of a tributarysignal, and transmit the overheads onto a tributary transmission line,thereby enabling a tributary far end transmission apparatus to detecterrors. It will be of course appreciated that the operation for the B2bytes on the demultiplexing side may be performed in a manner similar tothat on the multiplexing side, i.e., the calculation of k may beperformed in the overhead multiplex unit 130, or the calculation of kand the inversion of bits may be collectively performed in the LOHinsertion units 80-1˜80-M.

The multiplexer, which is an embodiment of the transmission apparatus ofthe present invention described above, is configured such that, wheninformation on the system configuration is received from a networkmanagement unit or the like, not shown, the control unit 400 determinessettings for the overhead processing unit 300, the multiplexed signaltransmission/reception units 10-1˜10-M and 11, and so on to therebyenable the selection of the type of overheads to be passed through themultiplexer and the selection of the locations of undefined bytes intowhich the overheads are inserted.

FIG. 9 is a network configuration diagram illustrating an example of theconfiguration of a transmission network using the multiplexer of thepresent invention. More specifically, FIG. 9 illustrates in detail theconfiguration of a network in which the foregoing multiplexerillustrated in FIG. 5 is employed as the additionally installedmultiplexers E, F in the network configuration diagram illustrated inFIG. 4B. It should be noted that FIG. 9 illustrates an example in whichoverheads are transmitted from a multiplexer B to a multiplexer C, andthat the illustrated multiplexers according to the present inventiononly include the multiplexing side and the demultiplexing side requiredto the respective multiplexers.

The transmission network employing the multiplexers of the presentinvention comprises a multiplexer B2001 for multiplexing main signals totransmit a tributary multiplexed signal onto a tributary transmissionline 500; a multiplexer E2006 for further multiplexing tributarymultiplexed signals to transmit a high speed multiplexed signal onto ahigh speed signal transmission line 501; a multiplexer unit F2007 fordemultiplexing a high speed multiplexed signal received from the highspeed transmission line 501 to transmit tributary multiplexed signalsonto a tributary signal transmission line 502; and a multiplexer C2004for further demultiplexing the tributary multiplexed signals totributary main signals, wherein main signals processed by themultiplexer B2001 is transmitted to the multiplexer C2004, whileoverheads in tributary multiplexed signals are also transmitted betweenthe multiplexers B2001 and C2004 to perform administration andmaintenance operations for the transmission system.

Explaining in greater details, when the multiplexer B2001 generates atributary multiplexed signal by multiplexing main signals and addingoverheads to the multiplexed main signals, and transmits the tributarymultiplexed signal onto the tributary signal transmission line 500, themultiplexer E2006 terminates the overheads in the tributary multiplexedsignal, multiplexes the main signals, and generates overheads for a highspeed multiplexed signal, while it performs the overhead passingprocessing which constitutes a feature of the present invention. Aspreviously explained with reference to FIGS. 5-7, the passing processingis carried out by the tributary signal SOH termination unit 20 and thetributary signal LOH termination unit 30, the overhead processing unit300-1 comprising the overhead multiplex unit 110, the space switch unit200, and the overhead demultiplex unit 120, and the high speed signalLOH insertion unit 40 and the high speed signal SOH insertion unit 50,by selectively crossconnecting overheads in the tributary multiplexedsignal specified by the control unit 400 to insert the specifiedoverheads into specified locations in an overhead area of the high speedmultiplexed signal (see FIGS. 6 and 7). When specified overheads includethe B2 bytes, the B2-byte processing is also performed as describedabove.

The multiplexer F2007, which has received the high speed multiplexedsignal including the overheads to be passed, from the multiplexer E2006through the high speed transmission line 501, terminates the overheadsin the high speed multiplexed signal, demultiplexes main signals, andgenerates overheads for tributary multiplexed signals, while it performsthe overhead passing processing which constitutes a feature of thepresent invention. This passing processing, as previously explained, isthe reverse processing of the passing processing performed by themultiplexer E2006, wherein overheads for tributary multiplexed signalsincluded in the high speed multiplexed signal and specified by thecontrol unit 400 to be passed are selectively crossconnected andinserted into specified locations in the overhead area of the respectivetributary multiplexed signals. This overhead passing processing isperformed by the high speed signal SOH termination unit 60 and the highspeed signal LOH termination unit 70, the overhead processing unit 300-2comprising the overhead multiplex unit 130, the space switch 210, andthe overhead demultiplex unit 140, and the tributary LOH insertion unit80 and the tributary SOH insertion unit 90. When the specified overheadsinclude the B2 bytes, the B2-byte processing is also performed asdescribed above.

Thus, even in the transmission network in which the multiplexers E, Fhave been additionally inserted between the original multiplexers B andC, the foregoing configuration and operations enable the overheads inthe low passed multiplexed signals as well as main signals to betransmitted between the multiplexers B and C without being terminated atthe additional multiplexer E or F.

The multiplex transmission apparatus of the present invention can passarbitrary overheads in a multiplexed signal with the configuration andoperations described in connection with the foregoing embodiment. Inother words, even if a transmission system as illustrated in FIG. 4A ismodified to a new system as illustrated in FIG. 4B, the multiplexerdescribed in the foregoing embodiment, if employed for newly addedmultiplexers, passes overheads so far used between the multiplexers Band C without terminating them, so that the overheads can be used alsobetween the multiplexers B and C in the modified system. Thus, theadministration and maintenance operation capability between themultiplexers is not affected by the modification to the configuration ofthe transmission system. In addition, since the multiplexer of thepresent invention permits overheads to be used between any desiredmultiplexers, it is possible to provide a multiplexer which has higheradministration and maintenance operation capability, offers auser-friendly operability, and supports to build a flexible transmissionsystem.

Next, another embodiment of the multiplexer according to the presentinvention and an embodiment of a transmission system or a network usingthe multiplexer will hereinafter be described in detail with referenceto the accompanying drawings.

FIG. 10 is a block configuration diagram illustrating an embodiment ofan add drop multiplexer (hereinafter abbreviated as “ADM”) which is atransmission apparatus according to the present invention. FIGS. 11A and11B are network configuration diagrams illustrating examples of theconfiguration of transmission networks using the ADM of the presentinvention.

The ADM of the present invention accommodates a plurality of tributarymultiplexed signals comprising overheads and main signals multiplexedtherewith and two high speed multiplexed signals comprising overheadsand main signals multiplexed therewith, and performs the processing suchas termination, replacement, and so on for the overheads in therespective multiplexed signals. In addition, the ADM inserts a pluralityof tributary multiplexed main signals into high speed multiplexed mainsignals (add), branches a plurality of tributary multiplexed mainsignals from high speed multiplexed main signals (drop), crossconnectshigh speed multiplexed main signals with each other (cross-connect), andpasses the high speed multiplexed main signals (through). Similarly tothe aforementioned embodiment, the tributary multiplexed signals aretransmitted through OC12s, while the high speed multiplexed signals aretransmitted through OC-192s. The ADM performs the processing for themain signal and the overhead processing as defined in SONET, and alsopasses a portion of overheads in the multiplexed signals inputtedthereto so that the passed overheads are used by a far end multiplexer.Then, a network employing the ADMs has the ADMs connected to each otherthrough high speed transmission spans (OC-192) in a linear configuration(FIG. 11A) or in a ring configuration (FIG. 11B). In addition,transmission apparatuses such as multiplexers are connected to the ADMsthrough tributary transmission spans (OC12). With the configurationdescribed above, the ADMs perform the overhead passing processing inaccordance with the present invention to transmit and receive arbitraryoverheads in the tributary multiplexed signals between arbitrarymultiplexers, in addition to the main signal processing as mentionedabove to transmit and receive the main signals between the multiplexers,thereby building a highly flexible transmission system which allows themultiplexers within the network to freely transmit and receive theoverheads as well as the main signals therebetween, and provides ahigher administration and maintenance operation capability.

The configuration of the ADM is substantially the same as that of theaforementioned multiplexer except for a main signal insertion/separationunit 105 additionally provided for performing add, drop, cross-connect,and through operations for the main signals. The remaining functionalblocks used in FIG. 10 are the same as corresponding ones in theaforementioned multiplexer (in FIG. 10, the same functional blocks asthose in FIG. 6 are designated the same reference numerals), except forthe location and number thereof which are modified to be adapted to theADM. In the following explanation, only the configuration and operationsdifferent from the aforementioned multiplexer will be described inparticular.

Since a high speed transmission/reception unit 11 is used to connect theADMs with each other through a high speed transmission span (see FIGS.11A, 11B) in this embodiment, two high speed transmission/receptionunits 11, i.e., a west side unit 11-1 and an east side unit 11-2, areprovided in each ADM so as to be connected to ADMs on both sides. Also,a main signal insertion/separation unit 105 is added between the highspeed signal transmission/reception units 11-1, 11-2 and a main signalmultiplex/demultiplex convertor unit 100 so that the high speed signaltransmission/reception units 11-1, 11-2 can be connected to tributarysignal transmission/reception units 10-1˜10-M, and the high speed signaltransmission/reception units 11-1, 11-2 can be connected to each otherin order to perform the main signal processing as mentioned above.

Further, the ADM is also adapted to pass overheads from a high speedmultiplexed signal to another such that a space switch unit 200 of anoverhead processing unit 300 selectively crossconnects overheads to bepassed, which have been received from one of the high speed signaltransmission/reception units (for example, the East side unit) throughan overhead multiplex unit 130, and transmits the crossconnectedoverheads to the other high speed transmission/reception unit (forexample, the WEST side unit) which inserts the overheads to be passedinto specified bytes in an overhead area of a high speed multiplexedsignal.

Furthermore, when overheads to be passed from a high speed multiplexedsignal to another includes information on the B2 bytes, a LOH insertionunit 40 of the high speed signal transmission/reception unit 11 does notperform the bit inversion of the B2 bytes as does the LOH insertion unit80 of the tributary signal transmission/reception unit 10 in theaforementioned multiplexer, and instead adds the number of errors i (theresult of termination of the B2 bytes), which have occurred on anincoming high speed transmission line, to a received number of errors jto derive a total number of errors k which is transmitted as it is. Inthe alternative, the configuration for detecting transmission errors inthis overhead transmission/reception interval may be implemented by aconfiguration utilizing a tandem connection, later described.

The ADM is also configured to rely on a control unit 400 which indicatesto each functional block the types and locations to be inserted foroverheads to be passed, such that each functional block responsivelyperforms the crossconnecting, selection, and insertion of the overheads.The control unit 400, in turn, is coupled to receive the controlinformation from a network management unit 2017 illustrated in FIGS. 11Aand 11B. Specifically, the network management unit 2017 appropriatelyindicates to each ADM the types and locations to be inserted foroverheads to be passed, so as to prevent conflicts or contradiction,thereby allowing overheads as well as main signals to be freelytransmitted and received between multiplexers within the network.

As described above, according to the present invention, overheads can bepassed through arbitrary multiplexers so that they may be used betweenarbitrary multiplexers likewise in the ADM described in the foregoingembodiment as well as in a transmission network or a transmission systemwhich employs the ADMs. It is therefore possible to provide atransmission system which is free from a change in administration andmaintenance operation capability due to a modification to a systemconfiguration, i.e., which is superior in improved administration andmaintenance operation capability, flexible, and highly usable.

Next explained in the following is a configuration for detectingtransmission errors occurring in a transmission interval betweenmultiplexers which transmits and receives overheads, with reference toanother embodiment different in configuration from the foregoingembodiments. Specifically, this embodiment is equivalent to aconfiguration of a transmission system adopting SONET or SDH whichnotifies transmission errors occurring in an interval from an overheadtransmitting multiplexer to an overhead receiving multiplexer using atandem connection standardized by ANSI or ITU-T, i.e., a configurationwhich passes the B2 bytes through intervening multiplexers. Thus, in theaforementioned multiplexer and ADM, any configuration may be utilized.

FIGS. 12A and 12B are operation explanation diagrams for explaining aconfiguration for detecting transmission errors using a tandemconnection. More specifically, FIG. 12A illustrates the configurationaccording to this embodiment, and FIG. 12B illustrates the configurationfor detecting transmission errors which has been explained in connectionwith the aforementioned multiplexer or ADM. FIG. 13 is a networkconfiguration diagram illustrating the configuration of a transmissionnetwork using a tandem connection. With reference to these drawings, theconfiguration for detecting transmission errors using a tandemconnection according to the present invention will be explained below incomparison with the embodiments described above.

As illustrated in FIG. 12B, the previously described embodiments areconfigured to pass the B2 bytes through a certain multiplexer such thaterrors are detected using the B2 bytes in a transmission intervalbetween different multiplexers. For this purpose, each multiplexer whichpasses the B2 bytes terminates the B2 bytes, detects the number oferrors i, adds the number of errors i to the number of errors j notifiedfrom a source multiplexer to derive a total number of errors k, andtransmits the total number of errors k. Then, the last multiplexer whichpasses the overheads, generates B2 bytes from the final total number oferrors (k′ in FIG. 12B), which have been added in the respectiveintervening multiplexers, and inverts bits of the B2 bytes to notifytransmission errors which have occurred during the transmission from anoverhead originating multiplexer to a destination multiplexer.

In a transmission system adopting SONET or SDH, the management of a pathis basically carried out between a source unit and a destination unit.However, if a path from a source Path Terminating Equipment (PTE) 4000-1to a destination PTE 4000-2 passes through network regions which aremanaged by different management schemes as illustrated in FIG. 13 (inthis embodiment, the path passes through network management regions1-3), it is necessary to independently manage the path in eachmanagement region to locate a region in which a failure has occurred.Thus, as stipulated in ANSI standard T1. 150 or ITU-T standard G. 707,an interval between both boundaries of a management region including aplurality of continuously connected Line Terminating Equipments (LTEs)and lines is defined as a tandem connection for which a managementmethod is defined. Specifically, one of a plurality of path overheadsPOHs included in a payload illustrated in the frame structure diagram ofFIG. 1 is used. Transmission errors are managed using B3 byte in thethird row for detecting errors in a path and Z5 byte in the ninth rowwhich is a byte for managing a tandem connection. Explaining, as anexample, the detection of transmission errors in the tandem connectionin the management region l, an LTE 4001 monitors the B3 byte for thenumber of errors l which have occurred on a path from the source PTE4000-1 to the LTE 4001, and inserts the number of errors l into the Z5byte and transmits the multiplexed signal to a LTE 4002. The LTE 4002again monitors the B3 byte for the number of errors l′ which haveoccurred on a path from the source PTE 4000-1 to the LTE 4002, andsubtracts the number of errors l received through the Z5 byte from thenumber of errors l′ to manage the number of errors which have occurredin the tandem connection.

In the configuration described in this embodiment for detectingtransmission errors occurring in a transmission interval betweenmultiplexers which transmits and receives overheads, the firstmultiplexer 2030 which first passes overheads in a tributary multiplexedsignal is regarded as an entrance multiplexer of the tandem connection,and the last multiplexer 2032 which passes the overheads in thetributary multiplexed signal is regarded as a terminal multiplexer, asillustrated in FIG. 12A, so that the number of errors is communicatedutilizing a tandem connection management method using the B3 byte andthe Z5 byte as mentioned above.

Specifically, the multiplexer 2030 encodes the number of errors (j)detected after terminating the B2 bytes of the tributary multiplexedsignal, inserts the encoded number of errors into a specified byte in anoverhead area of a high speed multiplexed signal, and transmits the highspeed multiplexed signal onto a transmission line to the destinationmultiplexer (3001, 3002), in a manner similar to the aforementionedembodiments. Also, the multiplexer 2030 checks the B3 byte for thenumber of errors which have occurred on a path up to the multiplexer2030 itself, and inserts the detected number of errors (l) into the Z5byte to transmit the number of errors (3003).

An intervening multiplexer 2031 which passes overheads therethrough onlypasses the received number of errors (3004, 3002), and does not add thenumber of errors (i), detected on a line between the multiplexers andnotified through the B2 bytes, to the number of errors (l), as does themultiplexers of the aforementioned embodiment (see FIG. 12B). Of course,the termination of the B2 bytes (error detection on the reception sideand generation of parities on the transmission side) is performed asusual (in conformity to the standard), which, however, is processedindependently of the overhead passing processing explained in thisembodiment. Also, since the B3 byte and the Z5 byte may be checkedbetween paths, that is, on the root between the Path TerminatingEquipments (PTEs) 4000-1 and 4000-2 of FIG. 13, the transmissionapparatus of this embodiment does not require other processing (checkfor the number of errors) except for passing these bytes as the mainsignals.

The multiplexer 2032 extracts the number of errors (j) transmitted fromthe multiplexer 2030 (3004). Also, the B3 byte is checked as explainedabove, and the value of the received Z5 byte (l) is subtracted from thenumber of errors (l′) occurring on the path up to the multiplexer 2032to derive the number of transmission errors (l′-l, i.e., the number oferrors equal to i+i′ in FIG. 12B) which has occurred on a transmissionpath between the multiplexers 2030 and 2032 (tandem connection) (3005).Then, the received number of errors (j) and the calculation result(l′-l) are added to derive the number of errors (k′) which have occurredon a transmission interval from the source multiplexer to themultiplexer 2032 in a manner similar to the aforementioned embodiment(3001), and the number of bits equal to k′ in generated B2 parity bitsare inverted and transmitted to a destination multiplexer 2033 (3006).

The configuration and method as described above also provide a resultsimilar to the aforementioned embodiment in which the B2 bytes arepassed through intervening multiplexers, thus making it possible tonotify a destination apparatus of transmission errors which haveoccurred on a transmission interval between the source and destinationmultiplexers which transmit and receive the overheads. Also, accordingto the configuration described above, an intervening multiplex whichpasses overheads therethrough need not perform calculations. Since thefirst and last multiplexers are only required to perform calculations,the amount of hardware can be reduced in an interval including a largenumber of multiplexers which pass overheads therethrough. One of theaforementioned configuration (FIG. 12B) and the configuration of thisembodiment (FIG. 12A) may be selected depending on the scale of aparticular network or system.

As described above, since a transmission network is built with themultiplexers and ADMs provided with the function of passing overheads,in accordance with the present invention, a modification to the networkconfiguration will not affect the administration and maintenanceoperation capability as has been often the case of the conventionaltransmission system. Also, since arbitrary overheads can be transmittedand received between arbitrary multiplexers within a transmissionnetwork, a flexible network having a superior administration andmaintenance operation capability can be readily realized. Specifically,the orderwires E1, E2 may be transmitted and received between arbitrarymultiplexers to allow a craft man to make a speech communication. Inaddition, the data communication channels D1-D12 may be transmitted andreceived to set a variety of parameters and so on for multiplexers, thusmaking it possible to build a flexible transmission network which can bereadily modified in configuration. Particularly, in accordance withSONET, the D1-D12 are transmitted from a network management unit or thelike to make settings for respective multiplexers, in which case if theconfiguration of passing such communication channels D1-D12 throughintervening multiplexers is employed according to the present invention,data required for settings can be readily sent to a destinationmultiplexers without the need for the intervention of complicatedprocessing performed by a control unit of a multiplexer, as is the caseof the conventional multiplexers, each of which would have to onceterminate and again transmit overheads. It is therefore appreciated thatthe present invention is extremely effective in the maintenanceoperation management of a transmission network. Further, since theswitching control bytes K1, K2 for controlling the switching oftransmission lines may be transmitted and received to achieve theselection of a transmission line free from contradiction betweenmultiplexers, the network configuration can be promptly modified orreconfigured if a transmission line fails. This is also effective in themaintenance operation management for the transmission network. Fortransmission errors, although the B2 bytes cannot be directlytransferred between source and destination multiplexers, the number ofoccurring errors is reliably detected and notified, so that it ispossible to realize the management of the error ratio in a transmissioninterval equivalent to that achieved by the B2 bytes which aretransmitted and received between directly coupled source and destinationmultiplexers without any intervening multiplexer. It will be of courseappreciated that if other overheads illustrated in FIG. 3 are alsotransferred in a manner similar to the overheads explained above, theycan be utilized likewise for the administration and maintenanceoperation between multiplexers.

In the present invention, undefined bytes in an overhead area of amultiplexed signal defined by the standard as mentioned above areselected, and overheads to be passed through a transmission apparatusare inserted into the selected undefined bytes in the multiplexedsignal, and then transmitted in the multiplexed signal. In other words,in a transmission network or a transmission system, bytes to be used maybe previously determined before transmission and reception, or thepreviously explained data communication channels may be used to modifysettings of used bytes before transmitting and receiving these bytes.Since free settings can be made depending on the number of transmissionapparatuses and the amount of administration and maintenance operationinformation within a transmission network as long as undefined bytes areavailable, it is possible to provide a transmission apparatus and atransmission network which have an administration and maintenanceoperation capability high enough to flexibly cope with modifications innetwork configuration or administration and maintenance operation methodor with future modifications in the standards, if any.

According to the multiplex transmission apparatus and the multiplextransmission network of the present invention, desired transmissionapparatuses within a network are allowed to transmit and receiveoverheads for carrying information associated with administration andmaintenance operations, which have been terminated at each transmissionapparatus in a conventional transmission system, so that it is possibleto provide a transmission apparatus and a transmission network whichhave a high administration and maintenance operation capabilityindependent of modifications in network configuration or of an employedadministration and maintenance operation method.

What is claimed is:
 1. A multiplex transmission apparatus for receivinga first multiplexed signal comprising a first payload having a pluralityof main signals multiplexed therein and a first overhead bytes includinga plurality of first maintenance information associated withadministration and maintenance operations, performing terminationprocessing for said first maintenance information and transmissionprocessing for the main signals in said first payload, thereafterconverting said first multiplexed signal into a second multiplexedsignal comprising a second payload having multiplexed therein said mainsignals which have been processed for transmission, and a secondoverhead bytes including a plurality of second maintenance informationassociated with the administration and maintenance operations, saidsecond maintenance information to be output to a far end communicationapparatus, and transmitting said second multiplexed signal; comprising:an extraction circuit for extracting predetermined maintenanceinformation from said first maintenance information; a cross-connectingcircuit for cross-connecting information extracted by said extractioncircuit; and insertion circuit means for inserting an output of saidcrossconnecting circuit into a predetermined location in said secondoverhead bytes, wherein said predetermined maintenance information insaid first multiplexed signal is transferred to said second multiplexedsignal.
 2. A multiplex transmission apparatus for receiving from aplurality of first transmission line first multiplexed signals eachcomprising a first payload having a plurality of main signalsmultiplexed therein and a first overhead including a plurality of firstmaintenance information associated with administration and maintenanceoperations, performing termination processing for said plurality offirst maintenance information and multiplexing of said plurality offirst payloads in a second payload, and converting said firstmultiplexed signals into a second multiplexed signals comprising secondoverhead bytes including a plurality of second maintenance informationassociated with the administration and maintenance operations to beoutput to a far end communication apparatus and said second payloadadded to said second overhead bytes, and transmitting said secondmultiplexed signal onto a second transmission line, said apparatuscomprising: an extraction circuit for extracting predeterminedmaintenance information from said plurality of first maintenanceinformation; a crossconnecting circuit for crossconnecting informationextracted by said extraction circuit; and an insertion circuit forinserting an output of said crossconnecting circuit into a predeterminedlocation in said second overhead bytes; wherein said predeterminedmaintenance information transmitted through said first transmission lineis transferred to said second transmission line.
 3. A multiplextransmission apparatus for receiving from a first transmission line afirst multiplexed signal comprising a first payload having a pluralityof main signals multiplexed therein and a first overhead including aplurality of first maintenance information associated withadministration and maintenance operations, performing terminationprocessing for said first maintenance information and demultiplexing ofsaid first payload to a plurality of second payloads, and convertingsaid first multiplexed signal into a plurality of second multiplexedsignals each comprising a plurality of second overhead bytes including aplurality of second maintenance information associated with theadministration and maintenance operations, said second maintenanceinformation being output to a far end communication apparatus, and oneof said demultiplexed second payloads, and transmitting said pluralityof second multiplexed signals onto a plurality of second transmissionlines, said apparatus comprising: an extraction circuit for extractingpredetermined maintenance information from said plurality of firstmaintenance information; a crossconnecting circuit for crossconnectinginformation extracted by said extraction circuit; and an insertioncircuit for inserting outputs of said crossconnecting circuit intorespective predetermined locations in said plurality of second overheadbytes, wherein said predetermined maintenance information transmittedthrough said first transmission line is transferred onto said pluralityof second transmission lines.
 4. A multiplex transmission apparatusaccording to any one of claims 2-3, wherein an overhead added to each ofsaid first multiplexed signals and said second multiplexed signalscomprises a section overhead and a line overhead defined inRecommendation G. 707 of International Telecommunication Union orStandard T. 105 of American National Standard Institute, and saidmultiplex transmission apparatus inserts maintenance informationincluded in a line overhead of said first multiplexed signals into apredetermined location in a section overhead or a line overhead of saidsecond demultiplexed signal.
 5. A multiples transmission apparatus forreceiving a first transmission frame having a plurality of signalsmultiplexed therein, performing demultiplexing and crossconnectprocessing for said multiplexed signals, thereafter multiplexingprocessed signals in a second transmission frame, and outputting saidsecond transmission frame, comprising: a receiver circuit for receivinga first transmission frame comprising a first payload including aplurality of main signals and a first overhead including a plurality ofadministration and maintenance operation information; a terminationcircuit for terminating said first overhead; a detector circuit, fordetecting a first number of errors which have occurred in said firsttransmission frame; a processing circuit for multiplexing/demultiplexingor cross-connecting said main signals; an error quantity processorcircuit for outputting a predetermined code value corresponding to saidfirst number of errors detected by said detector circuit; a generatorcircuit for generating a second overhead including a plurality ofadministration and maintenance operation information to be output to afar end communication apparatus, said second overhead including anoutput of said error quantity processor circuit; and a transmittercircuit for transmitting a second payload including an output of saidprocessing circuit and said second overhead output by said generatorcircuit as said second transmission frame.
 6. A multiplex transmissionapparatus for receiving a first transmission frame having a plurality ofsignals multiplexed therein, performing demultiplexing and crossconnectprocessing for said multiplexed signals, thereafter multiplexingprocessed signals in a second transmission frame, and outputting saidsecond transmission frame, comprising: a receiver circuit for receivinga first transmission frame comprising a first payload including aplurality of main signals and a first overhead including a plurality ofadministration and maintenance operation information; a terminationcircuit for terminating said first overhead; a detector circuit fordetecting a first number of errors which have occurred in said firsttransmission frame; an extractor circuit for extracting a predeterminedoverhead bytes in said first transmission frame; a processing circuitfor multiplexing/demultiplexing or cross-connecting said main signals;an error quantity processor circuit comprising: a convertor circuit forconverting a value of said predetermined overhead bytes extracted bysaid extractor circuit to a second number of errors; an adder circuitfor obtaining a third number of errors by adding said first number oferrors and said second number of errors; and an output circuit foroutputting a predetermined code value corresponding to said third numberof errors calculated by said detector circuit as an output of said errorquantity processor circuit; a generator circuit for generating a secondoverhead including a plurality of administration and maintenanceoperation information to be output to a far end communication apparatus,said second overhead including an output of said error quantityprocessor circuit; and a transmitter circuit for transmitting a secondpayload including an output of said processing circuit and said secondoverhead output by said generator circuit as said second transmissionframe.
 7. A multiplex transmission apparatus for receiving a firsttransmission frame having a plurality of signals multiplexed therein,performing demultiplexing and crossconnect processing for saidmultiplexed signals, thereafter multiplexing processed signals in asecond transmission frame, and outputting said second transmissionframe, comprising: a receiver circuit for receiving said transmissionframe comprising a first payload including a plurality of main signalsand a first overhead including a plurality of administration andmaintenance operation information; a termination circuit for terminatingsaid first overhead; a detector circuit for detecting a first number oferrors which have occurred in said first transmission frame; anextractor circuit for extracting a predetermined overhead bytes in saidfirst transmission frame; a processing circuit formultiplexing/demultiplexing or cross-connecting said main signals; anerror quantity processor circuit comprising: a convertor circuit forconverting a value of said predetermined overhead bytes extracted bysaid extractor circuit to a second number of errors; an adder circuitfor obtaining a third number of errors by adding said first number oferrors and said second number of errors; and an output circuit foroutputting said third number of errors calculated by said detectorcircuit as an output of said error quantity processor circuit; agenerator circuit comprising: an overhead generator circuit forgenerating a second overhead including a plurality of administration andmaintenance operation information to be output to a far endcommunication apparatus, said second overhead including an output ofsaid error quantity processor circuit; and an error insertion circuitfor inverting a value of each bits in an error detecting code in saidsecond overhead, where a number of inverted bits equal to said thirdnumber of errors output from said error quantity processor circuit; anda transmitter circuit for transmitting a second payload including anoutput of said processing circuit and said second overhead output bysaid generator circuit as said second transmission frame.
 8. A multiplextransmission apparatus for receiving from a first transmission line afirst multiplexed signal comprising a first payload having a pluralityof main signals multiplexed therein and an overhead including aplurality of first maintenance information associated withadministration and maintenance operations, performing terminationprocessing for said maintenance information and transmission processingfor said main signals in said payload, thereafter converting said firstmultiplexed signal into a second multiplexed signal comprising a secondpayload having multiplexed therein said main signals which have beenprocessed for transmission, and overhead bytes including a plurality ofsecond maintenance information associated with the administration andmaintenance operations, and transmitting said second multiplexed signalonto a second transmission line, wherein: said multiplex transmissionapparatus detects a first number of errors occurring on said firsttransmission line, inserts said first number of errors into an overheadbyte in said second multiplexed signal, and transfers said first numberof errors occurring on said first transmission line onto said secondtransmission line.
 9. A multiplex transmission apparatus according toclaim 8, comprising: an extraction circuit for extracting apredetermined overhead byte of said first multiplexed signal; a detectorcircuit for detecting a first number of errors occurred on said firsttransmission line; a transformation circuit for transforming a value ofsaid predetermined overhead byte extracted to a second number of errors;an adder circuit for adding said first number of errors and said secondnumber of errors; and a transmission line error transmitter circuit forinserting an output of said adder circuit into an overhead byte of saidsecond multiplexed signal.
 10. A multiplex transmission apparatusaccording to claim 8, comprising: an extraction circuit for extracting apredetermined overhead byte of said first multiplexed signal; a detectorcircuit for detecting said number of errors occurred on said firsttransmission line; a transformation circuit for transforming a value ofsaid predetermined overhead byte extracted to a second number of errors;an adder circuit for adding said first number of errors and said secondnumber of errors; and a transmission line error transmitter circuit forpreviously adding transmission line errors corresponding to an output ofsaid adder circuit to an error detecting code of said second multiplexedsignal.
 11. A multiplex transmission apparatus according to any one ofclaims 5-10, wherein said first number of errors are calculated based onB2 bytes or B3 bytes defined in Recommendation G. 707 of InternationalTelecommunication Union or Standard T1. 105 of American NationalStandard Institute.
 12. A multiplex transmission network comprising: aplurality of transmission lines each for transmitting transmissionframes each having a plurality of signals multiplexed therein; and aplurality of multiplex transmission apparatuses each for receiving saidtransmission frames from any of said transmission lines, performingtransmission processing for said multiplexed signals, and transmittingsaid processed signals in a transmission frame, wherein: saidtransmission frame comprises a payload having a plurality of mainsignals multiplexed therein and an overhead including a plurality ofadministration and maintenance information, and each of said multiplextransmission apparatuses comprises: a receiver circuit for receivingsaid transmission frame; a termination circuit for terminating saidoverhead; a transmission processing circuit formultiplexing/demultiplexing or cross-connecting said main signals insaid payload; an extraction circuit connected to said terminationcircuit for extracting predetermined bytes in said received overhead; acrossconnecting circuit for crossconnecting bytes output by saidextraction circuit; a generator circuit for generating said overheadincluding a plurality of administration and maintenance operationinformation to be output to a far end communication apparatus, saidoverhead including an output of said crossconnecting circuit; and atransmitter circuit for transmitting a payload including an output ofsaid transmission processing circuit and the overhead output by saidgenerator circuit as the transmission frame.
 13. A multiplextransmission network comprising: a plurality of transmission lines eachfor transmitting a multiplexed signal comprising a payload having aplurality of main signals multiplexed therein and overhead bytesincluding a plurality of maintenance information associated withadministration and maintenance operations; and a plurality of multiplextransmission apparatuses each for receiving said multiplexed signal fromany of said transmission lines, performing termination processing forsaid maintenance information and transmission processing for said mainsignals in said payload, and converting said multiplexed signal into adifferent multiplexed signal comprising a payload including said mainsignals, which have been processed for transmission, and overhead bytesincluding a plurality of different maintenance information associatedwith the administration and maintenance operations added to said mainsignals, wherein: said each multiplex transmission apparatus comprisesan overhead transfer circuit including an extraction circuit forextracting predetermined maintenance information from said plurality ofmaintenance information, and an insertion circuit for crossconnectingmaintenance information output by said extraction circuit and insertingsaid maintenance information into a predetermined location in theoverhead bytes of said different multiplexed signal to be transmitted,and another multiplexer connected between arbitrary multiplextransmission apparatuses through said plurality of transmission linespasses said predetermined maintenance information therethrough usingsaid overhead transfer circuit, such that said predetermined maintenanceinformation is transmitted and received between said arbitrary multiplextransmission apparatuses.
 14. A multiplex transmission networkcomprising: a plurality of transmission lines each for transmitting atransmission frame having a plurality of signals multiplexed therein;and a plurality of multiplex transmission apparatuses each for receivingsaid transmission frame from any of said transmission lines, performingtransmission processing for said multiplexed signals, and transmittingsaid processed signals in a transmission frame, wherein: saidtransmission frame comprises a payload having a plurality of mainsignals multiplexed therein and an overhead including a plurality ofadministration and maintenance information, and each of said multiplextransmission apparatuses comprises: a receiver circuit for receiving afirst transmission frame; a termination circuit for terminating a firstoverhead in said first transmission frame; a detector circuit, fordetecting a first number of errors which have occurred in said firsttransmission frame; a transmission processing circuit formultiplexing/demultiplexing or cross-connecting main signals in a firstpayload in said first transmission frame; an error quantity processorcircuit for outputting a predetermined code value corresponding to saidfirst number of errors detected by said detector circuit; a generatorcircuit for generating a second overhead including a plurality ofadministration and maintenance operation information to be output to afar end communication apparatus, said second overhead including anoutput of said error quantity processor circuit; and a transmittercircuit for transmitting a second payload including an output of saidtransmission processing circuit and said second overhead output by saidgenerator circuit as a second transmission frame.
 15. A multiplextransmission network comprising: a plurality of transmission lines eachfor transmitting a transmission frame having a plurality of signalsmultiplexed therein; and a plurality of multiplex transmissionapparatuses each for receiving said transmission frame from any of saidtransmission lines, performing transmission processing for saidmultiplexed signals, and transmitting said processed signals in atransmission frame, wherein: said transmission frame comprises a payloadhaving a plurality of main signals multiplexed therein and an overheadincluding a plurality of administration and maintenance information, andeach of said multiplex transmission apparatuses comprises: a receivercircuit for receiving a first transmission frame; a termination circuitfor terminating a first overhead in said first transmission frame; adetector circuit for detecting a first number of errors which haveoccurred in said first transmission frame; an extractor circuit forextracting a predetermined overhead bytes in said first transmissionframe; a transmission processing circuit for multiplexing/demultiplexingor cross-connecting main signals in a first payload in said firsttransmission frame; an error quantity processor circuit comprising: aconvertor circuit for converting a value of said predetermined overheadbytes extracted by said extractor circuit to a second number of errors;an adder circuit for obtaining a third number of errors by adding saidfirst number of errors and said second number of errors; and an outputcircuit for outputting a predetermined code value corresponding to saidthird number of errors calculated by said detector circuit as an outputof said error quantity processor circuit; a generator circuit forgenerating a second overhead including a plurality of administration andmaintenance operation information to be output to a far endcommunication apparatus, said second overhead including an output ofsaid error quantity processor circuit; and a transmitter circuit fortransmitting a second payload including an output of said transmissionprocessing circuit and said second overhead output by said generatorcircuit as a second transmission frame.
 16. A multiplex transmissionnetwork comprising: a plurality of transmission lines each fortransmitting a transmission frame having a plurality of signalsmultiplexed therein; and a plurality of multiplex transmissionapparatuses each for receiving said transmission frame from any of saidtransmission lines, performing transmission processing for saidmultiplexed signals, and transmitting said processed signals in atransmission frame, wherein: said transmission frame comprises a payloadhaving a plurality of main signals multiplexed therein and an overheadincluding a plurality of administration and maintenance information, andeach of said multiplex transmission apparatuses comprises: a receivercircuit for receiving a first transmission frame; a termination circuitfor terminating a first overhead in said first transmission frame; adetector circuit for detecting a first number of errors which haveoccurred in said first transmission frame; an extractor circuit forextracting a predetermined overhead bytes in said first transmissionframe; a transmission processing circuit for multiplexing/demultiplexingor cross-connecting main signals in a first payload in said firsttransmission frame; an error quantity processor circuit comprising: aconvertor circuit for converting a value of said predetermined overheadbytes extracted by said extractor circuit to a second number of errors;an adder circuit for obtaining a third number of errors by adding saidfirst number of errors and said second number of errors; and an outputcircuit for outputting said third number of errors calculated by saiddetector circuit as an output of said error quantity processor circuit;a generator circuit comprising: an overhead generator circuit forgenerating a second overhead including a plurality of administration andmaintenance operation information to be output to a far endcommunication apparatus, said second overhead including an output ofsaid error quantity processor circuit; and an error insertion circuitfor inverting a value of each bits in an error detecting code in saidsecond overhead, where a number of inverted bits equal to said thirdnumber of errors output from said error quantity processor circuit; anda transmitter circuit for transmitting a second payload including anoutput of said transmission processing circuit and said second overheadoutput by said generator circuit as a second transmission frame.
 17. Amultiplex transmission network comprising a plurality of transmissionlines each for transmitting a first multiplexed signal comprising afirst payload having a plurality of main signals multiplexed therein andoverhead bytes including a plurality of maintenance informationassociated with administration and maintenance operations, and aplurality of multiplex transmission apparatuses each for receiving afirst multiplexed signal from any of said transmission lines, performingtermination processing for said maintenance information and transmissionprocessing for said main signals in said payload, converting saidmultiplexed signal into a second multiplexed signal comprising a secondpayload including said main signals which have been processed fortransmission and overhead bytes including a plurality of differentmaintenance information associated with administration and maintenanceoperations added to said payload, and transmitting said secondmultiplexed signal to another transmission line, wherein: said pluralityof multiplex transmission apparatuses are a first multiplex transmissionapparatus comprising a detector circuit for detecting a number of errorson a transmission line on a reception side, and an error quantityprocessing circuit for inserting said number of errors into an overheadbyte in said second multiplexed signal which is output to a transmissionline on a transmission side, said first multiplex transmission apparatustransferring said number of errors occurring on said transmission lineon the reception side onto the transmission line on the transmissionside; or a second multiplex transmission apparatus comprising anextraction circuit for extracting said number of errors transferred bysaid first multiplex transmission apparatus, a detector circuit fordetecting a number of transmission line errors on a transmission line ona reception side, an adder circuit for adding an output of saidextraction circuit and an output of said detector circuit, and atransmitter circuit for previously inserting errors to an errordetecting code for a far end transmission apparatus, where a number ofinserted errors is equal to an output from said adder circuit, and fortransmitting said error detecting code onto a transmission line on atransmission side, and said multiplex transmission network notifiestransmission line errors occurring between arbitrary multiplextransmission apparatuses through said first and second multiplextransmission apparatuses and a plurality of transmission lines.
 18. Amultiplex transmission network according to claim 17, furthercomprising, as said multiplex transmission apparatus, a third multiplextransmission apparatus comprising an extraction circuit for extractingsaid number of errors transferred by said first or third muliplextransmission apparatus, a detector circuit for detecting a number oftransmission line errors on a transmission line on a reception side, anadder circuit for adding an output of said extraction circuit and anoutput of said detector circuit, and a transmitter circuit fortransferring an output of said adder circuit onto a transmission line ona transmission side, wherein the number of transmission line errorsoccurring between arbitrary multiplex transmission apparatuses isnotified in said multiplex transmission network comprising said thirdmultiplex transmission apparatus located between said first and secondmultiplex transmission apparatuses.
 19. A multiplex transmission networkcomprising a plurality of transmission lines each for transmitting amultiplexed signal comprising a payload having a plurality of mainsignals multiplexed therein and overhead bytes including a plurality ofmaintenance information associated with administration and maintenanceoperations, and a plurality of multiplex transmission apparatuses eachfor receiving said multiplexed signal from any of said transmissionlines, performing termination processing for said maintenanceinformation and transmission processing for said main signals in saidpayload, thereafter converting said multiplexed signal into a differentmultiplexed signal comprising a payload including said main signalswhich have been processed for transmission and overhead bytes includinga plurality of different maintenance information associated with theadministration and maintenance operations added to said payload, andtransmitting said different multiplexed signal to another transmissionline, wherein: each of said plurality of multiplex transmissionapparatuses is: a first multiplex transmission apparatus comprising adetector circuit for detecting a number of errors on a transmission lineon a reception side, and an error quantity processing circuit forinserting said number of errors into an overhead byte in saidmultiplexed signal which is output to a transmission line on atransmission side, said first multiplex transmission apparatustransferring said number of errors occurring on said transmission lineon the reception side onto the transmission line on the transmissionside; or a second multiplex transmission apparatus comprising anextraction circuit for extracting said transferred number of errors, anda transfer circuit for transferring an output of said extraction circuitto the transmission line on said transmission side; or a third multiplextransmission apparatus comprising an extraction circuit for extractingsaid transferred number of errors, a detector circuit for detecting anumber of transmission line errors on a transmission line on a receptionside, an adder circuit for adding an output of said extraction circuitand an output of said detector circuit, and a transmitter circuit forpreviously inserting errors to an error detecting code for a far endtransmission apparatus, where a number of inserted errors is equal to anoutput from said adder circuit, and for transmitting said errordetecting code onto a transmission line on said transmission side, and anumber of transmission line errors occurring between an arbitrary firstmultiplex transmission apparatus and an arbitrary third multiplextransmission apparatus is notified in said multiplex transmissionnetwork comprising said first, second, and third multiplex transmissionapparatuses and the plurality of transmission lines.
 20. A multiplextransmission network according to any one of claims 17-19, whereininformation on said number of errors and said number of transmissionline errors notified between said multiplex transmission apparatuses isinformation corresponding to transmission line errors processed by B2bytes or B3 bytes defined in Recommendation G. 707 of InternationalTelecommunication Union or Standard T1. 105 of American NationalStandard Institute.
 21. A signal processing method for a multiplextransmission apparatus for receiving a first transmission frame having aplurality of signals multiplexed therein, performing demultiplexing andcrossconnect processing for said multiplexed signals, multiplexing saidprocessed signals in a second transmission frame, and outputting saidsecond transmission frame, said method comprising the steps of:receiving said first transmission frame comprising a first payloadhaving a plurality of main signals multiplexed therein and firstoverhead bytes including a plurality of maintenance informationassociated with administration and maintenance operations; terminatingsaid first overhead bytes; performing multiplexing/demultiplexing andcrossconnect processing for said main signals in said first payload;selecting predetermined maintenance information from said first overheadbytes; crossconnecting said selected maintenance information; generatingsecond overhead bytes including a plurality of maintenance information,associated with the administration and maintenance operations, to beoutput to another multiplex transmission line, said second overheadbytes including said crossconnected information; and transmitting asecond payload including main signals performed at said performingmultiplexing/demultiplexing and crossconnect processing and said secondoverhead bytes as said second transmission frame.
 22. A signalprocessing method for a multiplex transmission apparatus for receivingfrom a first transmission line a first multiplexed signal comprising afirst payload having a plurality of main signals multiplexed therein andfirst overhead bytes including a plurality of first maintenanceinformation associated with administration and maintenance operations,performing termination processing for said maintenance information andtransmission processing for said main signals in said first payload,converting said first multiplexed signal into a second multiplexedsignal comprising a second payload having multiplexed therein said mainsignals which have been processed for transmission and second overheadbytes including a plurality of second maintenance information associatedwith the administration and maintenance operations, and transmittingsaid second multiplexed signal onto a second transmission line, saidmethod comprising the steps of: selecting predetermined maintenanceinformation from said first overhead bytes inputted from said firsttransmission line; crossconnecting said selected maintenanceinformation; and selecting a location in said second overhead bytes forinserting said crossconnected maintenance information thereinto, andtransferring said second multiplexed signal onto said secondtransmission line. wherein said multiplex transmission apparatus passespredetermined maintenance information from said first maintenanceinformation.
 23. A method of operating a multiplex transmission networkcomprising a plurality of transmission lines each for transmitting amultiplexed signal comprising a payload having a plurality of mainsignals multiplexed therein and overhead bytes including a plurality ofmaintenance information associated with administration and maintenanceoperations, and a plurality of multiplex transmission apparatuses eachfor receiving said multiplexed signal from any of said transmissionlines, performing termination processing for said maintenanceinformation and transmission processing for said main signals in saidpayload, thereafter converting said multiplexed signal into a differentmultiplexed signal comprising a payload including said main signalswhich have been processed for transmission and overhead bytes includinga plurality of different maintenance information associated with theadministration and maintenance operations added to said payload, andtransmitting said different multiplexed signal to another transmissionline, said method comprising the steps of: selecting from said pluralityof multiplex transmission apparatuses multiplex transmission apparatuseswhich transmit and receive said maintenance information and multiplextransmission apparatuses which pass said maintenance informationtherethrough; selecting predetermined maintenance information to bepassed as a transmission side multiplexed signal from said maintenanceinformation of a reception side multiplexed signal in said selectedmultiplex transmission apparatuses; extracting the selected maintenanceinformation from said received overhead bytes in said selected multiplextransmission apparatuses; crossconnecting said extracted maintenanceinformation in said selected multiplex transmission apparatuses; andselecting a location for inserting said crossconnected maintenanceinformation in said overhead bytes of said multiplexed signal to betransmitted, inserting said crossconnected maintenance information intosaid location, and transferring said multiplexed signal onto atransmission line, wherein arbitrary maintenance information is passedthrough intervening multiplexers between arbitrary multiplextransmission apparatuses to allow said arbitrary multiplex transmissionapparatuses to transmit and receive the arbitrary maintenanceinformation therebetween.